1. Field of the Invention
The present invention relates to an X-ray high voltage generator and, more particularly, an X-ray high voltage generator used in a medical X-ray system and capable of promoting the safety of patients.
2. Description of the Prior Art
In recent years, as an X-ray high voltage generator for use in a medical X-ray system, an inverter type X-ray high voltage generator employing high power semiconductor devices has been spread with rapidity. As features of such inverter type X-ray high voltage generator, space saving due to reduction in size and weight of the high voltage generator which can be attained by making its working frequency higher, and higher efficiency which can be attained because X-ray tube voltage waveform, which is similar to a constant voltage, can be achieved by using either a single phase power supply or a three phase power supply may be considered.
FIG. 1 is a block circuit diagram showing an example of the inverter type X-ray high voltage generator for use in the medical X-ray system in the prior art.
As shown in FIG. 1, alternating current (AC) electric power supplied from the commercial power supply is rectified/smoothed by a full-wave rectifier 102 and a capacitor 103 into direct current (DC) electric power, and then supplied to an inverter circuit 104 which comprises high power semiconductor devices (high speed and large power switching devices). A fuse 105 is inserted to one end of the input side of the inverter circuit 104, and a current detector 106 is inserted to the other end of the inverter circuit 104.
DC electric power is converted into high frequency AC power (e.g., 10 kHz) by the inverter circuit 104, then a voltage of the high frequency AC power is increased into AC high voltage (e.g., 100 kV) by a high voltage transformer 107, then the AC high voltage is smoothed to DC high voltage (e.g., 140 kV) by a capacitor 109 and a high voltage rectifier 108 which is formed of silicon rectifier with a breakdown voltage of about 150 kV, etc., and then such DC high voltage is applied to an X-ray tube 110. A voltage dividing resistor 111 is connected in parallel with the capacitor 109. As a detection value of a tube voltage (i.e., detection value corresponding to the applied voltage to the X-ray tube), a voltage across the voltage dividing resistor 111 is fed back to an inverter driving circuit 112 which controls switching timing of the inverter circuit 104.
To the inverter driving circuit 112 are input a detection value of the inverter current detector 106, the detection value of the tube voltage, and a set value of the tube voltage and a set value (exposure time) of a timer, both being input respectively via a console (not shown) of the X-ray system.
In addition, an output of the inverter driving circuit 112 can drive four high speed and large power switching transistors constituting the inverter circuit 104.
However, there have been following disadvantages in the X-ray high voltage generator in the prior art.
More particularly, if any trouble of the inverter circuit 104 is caused, X-ray output from the X-ray tube 110 is interrupted to thus interfere with patient's diagnosis.
In particular, in the X-ray high voltage generator for use in a diagnostic system for the circulatory system, if the X-ray output is interrupted during catheter manipulation by the surgeon in operation, it becomes difficult for the surgeon to manipulate such catheter. As a result, danger to the subject (patient) would be increased and occasionally a subject's life-threatening situation would be brought about.